Temperature responsive circuit selector



y 7 1951 J. N. STEWART 2,560,829

TEMPERATURE masponsxvz cmcun SELECTOR Filed Oct. 8, 1945 INVHVTOR.

Patented July 17, 1951 UNITED STATES PATENT OFFICE TEMPERATURE RESPONSIVE CIRCUIT SELECTOR Application October 8, 1945, Serial No. 620,981

19 Claims.

This invention relates to circuit selectors, and more especially to means and apparatus tor the automatic selection oi measuring circuits such as those associated with thermocouples, in order that there may be obtained a measurement or controlling function based upon temperature or other property of that one of a plurality of measured objects which is characterized by the extreme oi the magnitude under measurement. The particular application of the present invention lies in the automatic control of temperature where there are involved a number of more or less separate objects or masses having their temperatures individually measured, and normally subject to variations following a common characteristic law. In such measurements it frequently becomes desirable to direct special attention to, or to effect control based upon, the temperature of that object which for any reason may depart from the value obtained upon the other objects. For example, in automatically control- 8 the temperature oi an aircraft engine, by means of the conventional cowl-flap control, it becomes important that the control be based upon the temperature attained by the hottest cylinder oi the engine; and, since it is quite possible that, owing to a variety of uniorseen conditions, any one of the engine cylinders may rise to a temperature exceeding that of the others, it is important that said cylinder be promptly selected ifrom the group and placed under surveillance. Similar conditions attend the operation of Diesel engines, wherein an excessive rise or tail of temperature characterizing the exhaust from any invidual cylinder demands immediate attention. ther applications wherein it becomes important that the maximum or the minimum at a group oi similarly varying temperatures be selected for purposes of measurement or control, will be found in catalyst recovery plants in the petroleum industry, in the regulation of oven temperatures in the baking industry, and at various locations in both the mechanical and the electrical elements of power plants.

It is an object of the present invention to provide means for automatically selecting from among a group of two or more condition-sensitive devices that one associated with said condition in its extreme magnitude, and operatively connecting said device to a measuring or controlling instrument, whereby to provide at said instrument a measure of said condition.

It is a further object to provide means whereby, upon the condition to which is exposed another or said devices than that connected to the above measuring instrument becoming the extreme of the group under measurement, connections will be changed whereby to substitute said other sensitive device for that formerly connected to said instrument.

It is a further object to provide means for effooting the above identified objects with a minimum number of electrical contacts in the measuring circuit.

The invention, in its more specific aspects, also comprises rovisions for utilizing, in conjunction with a group of two or more temperature sensitive devices individually and selectively connectable to a measuring or controlling instrument, a corresponding group of auxiliary sensitive devices adapted for action through a suitable electrical network to select that one of said firstnamed temperature sensitive devices which is associated with the highest or the lowest temperature, and connect it to the measuring instrument, leaving it so connected as long as it is measuring the extreme temperature, and changing the connection to correspond similarly with any other sensitive device in the group which may subsequently attain a temperature, higher or lower, as the case may be.

For purposes of explanation, the invention is considered in its application to comparison of the temperatures of a number of solid objects or masses (such, for example, as the cylinders of an internal combustion engine) but there is no intention of so limiting the invention; and it will be obvious that the principles are equally applicable to comparative determination of temperatures of fluid masses, such as furnace atmospheres, and flowing or confined gases or liquids.

In the drawings:

Fig. l is a diagrammatic representation oi a system embodying the principles of the invention as applied to the selection for association with a measuring instrument of that one of four thermocouples which is associated with th hottest of four independent objects whose temperatures are to be measured or regulated.

Fig. 2 shows a galvanometer-relay suited to the purposes of the invention.

Fig. 3 is a diagram of the system as applied to selection for measurement or control purposes of the thermocouple associated with the coolest of a group of objects whose temperatures are to be measured or regulated.

Referring now to Fig. l of the drawings, the numerals II, III, 30 and ill designate four separate objects or masses subject to temperature variation, and of which it is desired that the temperature of the hottest shall be measured by means of an instrument 50. Thermally associated with the four masses ill, 20, Ill and lil respectively are corresponding thermocouples ll, 2|, II, and ll, each adapted to develop an electromotive force representative of the temperature of the masses with which it is associated. Means, hereinafter to be described, are provided for selectively associating the thermocouples with the instrument i; and the present invention rests primarily in rendering such means efl'ective to select the hottest of said four masses and connecting the associated thermocouple to th exclusion of the other thermocouples, to the instrument 5!, whereby to cause said instrument to provide a measure of the temperature to which said selected thermocouple is exposed.

Designating the thermocouples H, 2|, Si and Ii as the "measuring couples," there are provided also four "auxiliary couples, I2. 22,, i2 and 42, associated respectively with the masses I0. 20, 30 and III in such a manner that their temperatures shall be as nearly as possible identical with those of the corresponding measuring couples. In correspondence with the four masses whose temperatures are to be measured, there are provided four mutually identical relays i3, 28, a and it, said relays having operating solenoids ll, 24, 34 and 44 respectively. Each of said relays has three sets of normally open contacts, designated as a, b and 0, respectively and one set of normally closed contacts as d. Thus, when solenoid ll of relay I8 is energized, contacts '30,, l3b. llc will be closed, while contact lid will be open. Upon deenergization of solenoid ll, the conditions of said contacts will be reversed, contact i311, i3b and lie being opened and lid being closed. The designation of contact elements in relays 13, 33 and 43 is exactly similar to that 0! the elements in relay II; and the performance of said relays upon energization or deenergization of their respective windings is identical with that of relay II.

A drum type selector switch 60 is provided with four banks of contacts i5, 25, 35 and 45. The bank I! comprises four sets of contacts l6, I1, I. and i9. Similarly the bank 25 comprises four sets of contacts 26, 21, 28 and 29; and the bank 35 comprises four sets of contacts 86, 31. 88, 3!; while the bank 45 comprises four sets of contacts 46, 41, It and 40. A contact drum II is provided with four contact members l8. l1, II and I9, and is adapted to be moved by means of a motor ll transversely of the contact banks II, ll. 35 and I, whereby successively to complete the circuits which the sets oi contacts comprise in said banks. Said motor II is preferably operable at substantially constant speed and may be in continuous operation over any desired period. For example, in the position shown in the drawings, the drum I! is clear of all contact banks, and all the corresponding circuits are open. If the drum ll) be moved toward the right as shown in the drawing, the contact element It will bridge the contact ii; the element 11 will bridge the contact i1; the element 18 will bridge the contact ll; and the element It will bridge the contact ill. It will be observed that the contact element II is set slightly behind the other three contact elements carried by the drum, so that contacts II. II and II are completed momentarily in advance of the completion of contact i) by contact element l1. As the drum is translated further to the right, its contact elements will engage in succession the contacts which are comprised in banks 28, I! and II, completing the circuits at these contacts in the same manner and sequence as the corresponding contacts constituting the bank II.

A relay II is provided with a normally open set of contacts a and normally closed set of contacts 83b, together with an operating solenoid 84. whereby, when the same is energized. contacts "a will be closed and 83b opened. with a reversal of conditions when the solenoid I4 is deenergized. A galvanometer 90, for details of which. reference may be had to Fig. 2, is provided with two electrically independent coils II and I! integrally mounted for deflection through a limited angle between magnet poles N and 8. said coil assembly carrying a movable contact 03 adapted for electrical engagement with a stationary contact H, but normally floating clear of the same when neither of the coils Si-M is energized. The coil ll, which may be referred to as the actuating coil," is adapted for connection to the thermocouple circuit in a manner presently to be described. The coil 92. which may he styled the holding coil," has a resistance relatively low in comparison with that of the relay solenoids ll. 24, etc., and has one terminal directly connected to the movable contact l3, and the other terminal free for connection to an outside circuit hereinafter to be set forth. The polarities assigned to the terminals of the two coils 9i and 92 as indicated in Fig. 2 are those of applied potentials which will cause the moving element to be deflected in a clockwise sense as shown, tending to bring the movable contact 93 into electrical engagement with the stationary contact 94.

The connections by means of which the electromotive forces developed in the several thermocouples are utilized, are as follows: the negative sides (as shown in the drawings) of measuring couples ii, 2|, 3i, and ll are connected to a common conductor II. and thereby to the negative terminal of the measuring instrument ill. The positive sides of said couples are connected by conductors ll, 62, 83, I4. respectively, to one side of each of the relay contact elements lib. 23b, 83b and "b, the free sides of said contact elements being connected to a common conductor 5! and thereby to the positive terminal of the instrument ill. The negative terminals of the auxiliary couples l2, 2!, 32 and 42 are connected to a common conductor 3 passing through the relay contacts i3d, 23d, lid and d in series and thence to a conductor 54. The positive terminals of the last-named group of couples are connected by means of conductors I, ii, 81 and SI, respectively, to one side of each of the relay contact elements 13a, 28a, 33a and "a, the free sides of said contact elements being connected to the conductor 64. To said conductor 54 are connected, also, one side of each of the selector contacts I6. 26, a. and 48, respectively, the tree sides of said contacts being connected to a common conductor 55 and thereby to the negative terminal of the coil Si in the galvanometer II. The selector contacts ll, 21, ll and l! have each one side tapped to the conductors I. M. II and GI respectively, the free sides of said contacts being connected to a common conductor l6, and thereby to the positive terminal of the galvanometer windinll I.

One terminal of cache! the relay solenoids I 4, 24, 3| and 44 is connected to a conductor ll forming the negative side of a source oi unidirectidhal current supply ii. The free terminals of said solenoids are respectively connected to conductors ll. I2, 63', and I. To said conductors are also respectively connected one side 01' each of the relay contacts He. He, lie, and c. and one side or each of the selector contacts II, II. 38 and ll. The free sides said relay contacts are connected to a common conductor II and thereby to one side 0! the normally closed contacts 83b in the relay 8!. One side of each of the selector contacts ll, 20, 3! and 4! is connected ta a common conductor 12 and thereby to a terminal oi the actuating solenoid I in the relay ll. The free terminal of said solenoid is connected by means of a conductor ll to the free side oi! the relay contact 83b, and also to the galvanometer contact 94. The free terminal or the galvanometer winding 92 is connected to the negative conductor 51; and bridged between said terminai'and the conductor I3 is a sparksuppressor comprising a suitably interconnected resistor l5 and capacitor 88. The free sides of the selector contacts ll. 2!, II, and I8 are connected to a common conductor I4, and thereby to one side of the normally-open relay contact Ila, the other side of said contact being connected to a conductor I5, forming the positive side of the current source El, and to which conductor also are connected the free sides of the selector contacts is, 29, 39, and 4!. Connected between the common conductor is and the positive conductor is a resistor is, the purpose of which will hereinafter be explained.

For the purpose of explaining the operation of the apparatus, as adapted to selection of the hottest of a group of thermocouples, it may be assumed that connections are made as shown in Fig. l, and that the motor H is running, causing the drum Iii to be moved continuously toward the right as shown in the drawing. With the drum II in the position indicated, where it engages none of the contact banks lS-IS etc., the relays ll, 21 etc, will all remain deenergized, so that only the lower contacts lid. 23:! etc. will be closed. The negative terminals 01' the auxiliary thermocouples ll, 22 etc., will be connected through conductor 51 and said lower contacts in series to conductor 54 and thereby to contact elements ll. 26 etc., in the respective banks. As there will be no complete circuit for either 01' the windings oi the gaivanometer 99, said galvanometer will stand with its contacts 93 and SI separated. Similarly, since no circuit is completed to the solenoid ll of the relay 8!, said relay will stand with its contact 83a open and its contact "I; closed.

It may now be assumed that the drum II has advanced to such a position that its movable contacts engage and thereby complete the circuit through the three upper contact elements in the bank l5, this including contacts Ii, H and II. The positive terminal oi auxiliary couple ll will thus be connected through contact elements i1 and contact member 11 to conductor 86, and thereby to the positive terminal of the winding ll in the galvanometer so. Conductor 54, which. as hereinbeiore pointed out, is at this time connected to conductor 53 and thereby to the negative terminals of the auxiliary couples i2. 22 etc. will be connected through contacts ii and contact element Ii to the conductor 55, and thereby tothe negative terminal of the winding II. where- 6 by the voltage of couple 1! will be directly impressed upon said winding. The galvanometer moving element will be deflected in a clockwise senseasseeninthedrawing,wherebycontacts "andllwillbebmughtinto t,thercby providing a path from the negative conductor I! through the winding 02 o! the galvanometer and said contacts, in series with the solenoid ll of relay '3 to the conductor I2. wntact element II will also have cooperated with contacts II toconnect conductor 14 to conductor II, but because the contact Ila of the relay I3 is open, no "circuit throughsaid conductors will at this time be completed. The contact element II ml the drum ll being set slightly behind the eon-. tacts 16, TI and II. there is provided a short time interval in which the above conditiom may be established before further circuit modificationsareeilected.

Itmaynowbeassumedthatthedrumllhas p suiliciently far that the contact ll has engaged the contact elements I, thereby interconnecting conductors II and IS. It will beseen'that therehasnowbeenprovidedacmnplete path between the negative and positive sides of the circuit II through the cal winding l2 and relay solenoid II, in series with contacts I! and II. Current through the holding coil 82 will tend to-amplii'y the engaging pressure of the galvanometer contacts and eliminate such tendency to chattering as might result from the relatively weak torque derived only from the thermocouple current flowing in the winding M. The conductor 5! in series with the normally closed contacts lib will Immentarily provide an alternative connection, shunting the solenoid; but the resistor 60 will limit current through said path to an extent not to inhibit the operation of relay '3 by means of said solenoid. Upon actuation o! the relay 88. contact "b will be opened interrupting the shunt through the resistor II, and allowing the solenoid ll to carry the whole current which through the holding coil 02. Contacts 83a will be closed, connecting conductor II to the positive conductor II. and thereby. through contact element ll. congacts II. and conductor ll. providing a path for current from the source ll through the solenoid II in relay 83, thus energizing said relay. Energimtion oi the relay I! will cause contacts lid to be opened and contacts "a, lib and Re to be closed. Closing of contacts lib will connect the positive terminal 01 measuring couple H to conductor 52, thereby completing a circuit whereby the potential 01' said couple will be applied to the instrument IO. causing said instrument to provide a measure of the temperature of the object II with which the couples II and II are associated. Closingofthccontacts iiawilieonnecttothe conductor 54 the positive terminal of auxiliary couple I! instead of the negative terminal whose connection thereto was interrupted by the opening of contact lid. Closing of contacts lie will connect to the conductor 8! that terminal oi the solenoid M which was originally connected through conductors II and I4 to the positive conductor Ii. As the drum ll, carrying its contacts 16. II, II and I! continues to progress toward the right as seen in the drawing, the first three. and subsequently the last-named 01 said contacts will disengage their associated contact elements, opening the circuits which were completed therethrough. Opening 01' contacts I! and contacts i! will clear the winding ll-irom .the

couple i2, leaving the galvanometer it subject solelytotorquedevelopbysuchcurrentasmay be flowing through the winding 82. Opening of contacts I! will clear the circuit originally retor the solenoid II in the relay II; but contact Ilc will provide an alternative circuit for the same in series with the resistor I, whereby said relay will remain in an condition, so that the instrument II will continue to meamre the potential of the couple II as applied through the circuit hereinbefore specified, and including the relay contact lib.

As the contact I. is broken due to further progrefl of the drum II, the circuit through the gal holding coil l2 and the relay solenoid It will be interrupted. whereby the galvanmneter contacts will be separated. and relay contacts Ila and "b will revert to their normal condition of open and closed respectively. Noturtherchangeinconditlonswilltakeplace until the drum ll advances to a position where the several contacts carried thereby engage the contact elements constituting the bank I. Belay It having remained energized, the positive terminal of auxiliarly couple I! will remain connected through the contact "a to the condoctor ll, so that upon the engagement of contact element It by contact Ii this terminal will again be connected to the conductor It and thereby to one side of the galvanometer winding ti. At the same time, the positive terminal oi the auxiliary couple 2!, associated with the object II will be connected through conductor 6 and contact element 21 to conductor Ii and thereby to the other side of said Ealvanometer winding. As contact lid is open, the conductor I! will function solely as a common conductor between the auxiliary thermocouples. with the result that the couples i2 and II will be connected in series opposition, and their resultant potential impressed directly upon the galvanometer winding Ii. It will be observed, however, that, whereas, when the contact bank it was active. the conductor It was connected to the positive terminal of the couple II, the conductor will now be connected to the positive terminal of the couple 2!. while the positive terminal of the couple II will be connected to the conductor Ii. This. the eil'cct of the couple it upon the deilection of the galvanometer it will be the opposite of its original eilect. and the net influence o! the combined couple will depend in sense upon which of the two develops the higher potential. There are hence two alternatives of performance, depending upon whlch oi the objects ll and II (with which, respectively. are associated the couples i2 and I2) is at the higher temperature.

Itmaviirst be assumed that the object II is the hotter of the two, when the potential at the couple I} will predominate, and the net potential applied to the galvanometer coil Ii will he oi a polarity to deflect the movement in a sense opposite to the deflection hereinbefore described. thereby maintaining the contacts 03- separaterhand their circuit open. The relay solenoid .6 will thus remain deenergized, and the contacts Ila will not close. Therefore. subsequent closure of contacts 20 will not complete any circuit, so that the relay it will not be operated; and, the relay 63 remaining energised through its contacts lie, and locked in its actuated position, connections between the thermocouple ii and the imtrument it will remain undisturbed: and said ioctrmnmt will continue to provide a measure of the temperature of the object II to which temperature said thermocouple is exposed.

It may now be alternatively, that the relative temperatures of the objects I. and ii are interchanged from the above-described condition, the object II having become the hotter of the two, so that the potential developed by the couple 1! will be higher than that developed by the couple it. The net potential between the conductors Ii-J0. applied to the galvanometer coil ",willthenbeof apolarltyoppositetothat just described, and the galvanometer moving element will be deflected in a sense to bring into mutual engagement the contacts 03-. There will thus be provided a path including the normallyclosedrelaycontactsllbandthelocking contacts lie in the relay ll. whereby the low resistance holding coil 82 is bridged across the relay solenoid It; and, the current through the shunt circuit so formed being limited by the resistor it, the portion thereof flowing in the branch including the solenoid M will be reduced to such a low value as to release the moving element of the relay l3. causing the same to revert to its normal cleenergiaed condition.

Engagement of the contacts il-ll will also have provided a path between line conductors 51-" through relay solenoid It said path being complete, except for separation oi the contacts 2!, which as hereinbefore set forth, will have their closing delayed a short interval behind that ol the other contacts in the corresponding bank. M the last named contacts are brought into engagement by advance of the drum II. a circuit will be completed through the solenoid ll, energizing the same. opening the contacts lib and closing contacts Ila. Opening of the first-named of said contacts will further disrupt the bridging circuit already opened by the contacts ilc upon release oi the relay it, while closing of the contacts Ila will now complete a circuit through contacts 18, conductor I! and the relay solenoid ll. energizing the relay 23, opening its contacts 23d and closing its contacts 23a. 23b and 230. Closing of contacts 23b will connect the positive terminal oi measuring couple 2| to conductor 52, thereby completing a circuit whereby the potential of said couple will be applied to the measuring instrument 5|, causing said instrument to provide a measure of the temperature of the object it with which the couples 2| and 22 are associated. Closing of the contacts 23a will connect the positive terminal of auxiliary couple 2! to conductor it, thereby rendering said couple available for subsequent comparison with couple 3!. Closing of contact 230, as hereinbefore set forth in connection with the function of contact lie in relay It, will provide a locking circuit, whereby relay 23 will be maintained in an energized condition independently of the galvanometer contacts 83-.

It will be seen that in the operation of the apparatus as described. there is first provided a measure of the temperature of the hot object it, after which a comparison is made between the temperature of that object and the object 2|. If the object II is the hotter oi the two. the instrument ll continues to measure its temperature and ignore that of the object ll. If, on the other hand, the object 2! is the hotter, the measuring function of the instrument will be transierred to that object, and the temperature of the. object it will no longer be subjected to measurement. In the same manner, as the drum 1! is rogressively advanced to contact banks ll and II, the temperatures of the objects Ill and 40 will successively be compared with those immediately preceding them. and the instrument ll placed in operative connection with the hotter of each pair under comparison. Thus, as the cycle 01' operation determined by the advance of the drum II from one to another oi the contact banks is repeated, the instrument 50 will measure the temperature oi the hottest oi the several objects with which the thermocouples are associated, and will continue to provide a measure of a selected object until in the course of a cycle of operation another of said objects is found to have attained a higher temperature value, whereupon the connections 01' the instrument will be transferred to the thermocouple associated with that object, and will remain so as long as no higher temperature develops in the system.

In Fig. 3 is shown a diagram embodying such changes from the basic arrangement of Fig. l as are necessary to adapt the principles oi the invention to the selection of the coolest, rather than the hottest, of a group of thermocouples. In the interests 01' simplicity, there are shown only two oi a number oi masses with which said couples may be associated, there being the objects Ill and 20 of Fig. l, to which are presented couples II and I2, and 2| and 22, respectively. For ease in comparing the two systems, the revised diagram is shown as incorporating the relay 83 and the galvanometer an Fig. l, as well as elements of the drum selector switch ill, with its included contacting elements, the combination being operatively associated with the instrument 50 for the purposes to which said instrument is adapted.

Corresponding to the two masses or objects i0 and are provided two mutually identical relays B1 and 91 having operating solenoids l8 and 98 respectively. Each of said relays has three sets of normally open contacts. designated as a, b and 0, respectively. said contacts of either relay all being closed when the corresponding solenoid is energized.

The negative terminals of the measuring couples Ii and 2| are connected to a common conductor 96, and thereby to the negative terminal of the measuring instrument 50. The positive terminals of said couples are connected by means of conductors llll and I02 respectively to one side each of the relay contact elements 81b and 91b,

the free sides of said contact elements being connected to a common conductor 96, and thereby to the positive terminal of the instrument Bl. The negative terminals of the auxiliary couples l2 and 22 are connected to a common conductor 99, and the positive terminals of said last-named couples, by means of conductors I03 and Ill, respective- .U. to one side of each oi the relay contacts Ila and 91a. The selector contacts I! and 26 have each one side tapped to the conductors I" and I, respectively, the free sides of said contacts being connected to a common conductor Ill and thereby to the negative side of the actuating winding 9| in the galvanometer 90. The free sides of the relay contacts Old and 910 are connected to a common conducLor I05, and thereby to one side of each of the selector contacts H and 21, the free sides of said selector contacts being connected in turn by means of a common conductor I08 to the positive terminal of the galvanometer winding 9|.

One terminal 01' each of the relay solenoids ll and 98 is connected to a conductor l9 forming the negative side of the source of unidirectional current supply It. The tree terminals 01' said solenoids are respectively connected to conductors ll and II. to which conductors also are connected respectively one side of each of the relay contacts 81c and "c, and one side of each or the selector contacts II and 28. The free sides of said last-named relay contacts are connected to a common conductor l2, and thereby to one side of the normally closed contacts lib in the relay The tree sides oi selector contacts II and 2| are connected by means of a common conductor It! to one-side oi the normally open contacts Ila in the relay II, the other side of said relay contacts being connected to a common conductor Ill, forming the positive side of the current source II. and to which, also, are connected one side or each 01' the selector contacts ll and 20. The free sides of said last-named selector contacts are connected by a common conductor III to a terminal of the solenoid it in the relay '8. The free terminal of said solenoid is connected by means of a conductor lill to the free side of the relay contact 83b, and also to the galvanometer contact 94. As described in the previously disclosed embodiment oi the invention, the movable contact 93 in the galvanometer II is connected to one side oi. the holding coil '2; and the free terminal 01 said coil is connected to the negative conductor ll. Bridged between said terminal and the conductor H0 is a spark-suppressor comprising the resistor I! and capacitor l0 interconnected in the same manner as shown in Fig. l. A spring-opened manually-closed pushbutton switch III is connected between the conduetor II and the line conductor ill; and a current-limiting resistor H2 between the latter conductor and the conductor I2.

The operation of the form or the invention shown in Fig. 3 is essentially similar to-that of the form shown in Fig. l, with certain inherent diflerences due to selectivity being based on the cooler, rather than the hotter, of any two thermocouples under comparison. With connections made as shown, and voltage applied at the source 58, operation 01 the system is initiated by momentarily depressing the switch i I I, which causes line voltage to be applied to the solenoid ll energizing the relay II and closing its several contacts. A circuit from the measuring couple Ii will-be provided through the contacts 81b to the instrument 5|, which instrument will provide a measure 0! the temperature to which said couple 'is exposed. Contacts I'lc will provide a locking circuit in series with the resistor I l l, whereby. upon release of the push-button switch ill therelay I! will remain energized. With the selector drum II 'in the position indicated, no circuit will be completed through any of the selector contacts. with the result that no potential will be applied to the galvanometer 90, and the relay will stand with its contacts 93 and N separated. Thus, the relay is will remain deenergized, with its contacts 83a open and its contacts 83b closed. "As the drum ll moves to a position where its contact elements ll, H and I8 engage respectively the contacts It. I! and II, corresponding conductors will be interconnected. The contact II will provide a connection between conductors III and IIS whereby the positive terminal of the thermocouple l2 will be connected to the negative terminal of the coil ll in the galvanometer ll. At the same time, said positive terminal, through relay contact Ila and selector contacts I], will be cona,seo,saa

nected to the positive terminal of said galvanometer coil, whereby said cell will be short-circuited. and will remain so until with advance of the drum 1| the contact element I8 clears the contacts it. As the only complete circuit which can include the thermocouple i! must also include in opposition thereto the couple 22, interconnected therewith by means of conductor ill and since the selector contacts 20 and relay contacts l'la are both in an open condition, it follows that no circuit is completed for the thermocouple i2, and no potential applied to the winding Si in the galvanometer 90. As the drum ll advances to a position where contact element ll engages contacts II. the positive conductor I is connected to the conductor Ill, whereby one side of the solenoid N is placed directly in communication with the positive side or the power supply. Since the contacts in the galvanometer ll are open, however, no communication is provided between the solenoid I4 and the negative side of the power supply, so that the relay 83 remains deenergised.

Thus, until the selector drum Ill advances to a position of engagement with the contact bank is, the instrument II will continue to provide a measure of the temperature to which the couple H is exposed. As the contact elements on the drum ll engage respectively the contacts II, 21 and II in the bank 25, the contact 26 will provide a connection between the positive terminal of the couple u and the negative terminal of the galvanometer coil 81. The relay 81 having remained energized, the positive terminal of the couple I! will be connected through the selector contacts 21 to the positive terminal of the coil I. There will thus be applied to said coil a potential representing the difference in thermoelectromotive forces developed by the couples i2 and I2, and the deflection of the galvanometer moving element will depend in sense upon which of said electromotive forces predominates. If the voltage developed in the couple I! is the greater, signifying that the object II is at a higher temperature than the object III. the net potential in the thermocouple circuit. applied to the terminals of the coil 9| will be such as to deflect the moving element in a clockwise sense, closing the contacts Nl, whereas, if the voltage of the couple I! is the lesser. the potential applied to the galvanometer will be of opposite polarity, and said contacts will remain separated.

It may first be assumed that conditions are such that the couple I! is developing the higher thermoelectromotive force. Closing of the contacts 83-84 will provide through conductors l2, Ill and I8, and the normally closed contacts lib in the relay HI a shunt path around the relay solenoid in series with the resistor HI, whereby the iorce of said solenoid will be weakened to such an extent that the relay I1 is released, opening its three sets of contacts. Opening of contacts 81a will clear couple I! from its series opposition connection to the couple 2!. Opening of contacts llc clears the relay locking circuit, while opening of contacts llb serves to disconnect thermocouple II from the instrument SI. As the drum ll advances to a position where its contact element I9 engages the contacts 2!, the positive side of the power supply will again be connected to one side of the solenoid ll in the relay II. The galvanometer contacts "-94 being closed, and held closed by current therethrough flowing in the holding coil 82, there will be provided a complete circuit from the positive to the negative side of the supply through the solenoid I, energiizng the relay ll. opening its contacts 81b and closing its contacts c. There will now be completed a circuit including selector contacts 28, conductor Ill and II. and relay solenoid 98, whereby the relay 9'! will be energized and all three sets of its contacts closed. Closing of the contacts "I; will complete a circuit whereby the electromotive force developed in couple Ii-that associated with the cooler oi the two objects under measurement-will be applied to the terminals of the instrument ll and will be measured thereby. Contacts 91c will provide a locking circuit in series with the resistor ill. whereby the relay II will remain energized after interruption of the closing circuit. Closing of contacts l'la will set up a portion of a circuit between the positive terminal of the couple 2! and the positive terminal of the galvanometer coil ii in anticipation of the succeeding cycle to be established by advance of the drum 1|.

It may now be assumed, alternatively. that at the moment the couples II and 2! are thrown into series opposition by action of the contact elements carried by the drum It, the voltage developed by the latter couple is the greater, signifying that of the objects II and ll. the object II is the cooler. The voltage of the couple 2! predominating, the net potential applied to the terminals of the galvanometer coil II will be such as to maintain the contacts SI. 9| separated. so that the relay .1 will remain energized, and relay 83 will remain deenergized. Under this condition no change will take place in the connections to the instrument ill; and the latter will continue to provide a measure of the temperature to which the thermocouple ii is exposed. The operation as thus described may be extended to any number oi thermocouple groups similarly associated with masses or objects whose temperatures are to be selectively determined; and, as the selector drum advances from bank to bank of associated contacts, the temperature of each obiect will be compared with that of the object measured immediately beforehand, and that having the lower temperature selected for operative connection to the instrument 50, which will continue to provide a measure of the temperature of that object until in the course oi an operating cycle another of said objects is found to have attained a lower temperature, whereupon the connections of the instrument will be transferred to the couple associated with that obiect. and will remain so as long as there develops no lower temperature among the objects or masses under measurement.

The terms and expressions which I have employed are used as terms of description and not of limitation, and I have no intention, in the use of such terms and expressions, of excluding any equivalents of the features shown and described or portions thereof, but recognize that various modifications are possible within the scope of the invention claimed.

I claim:

1. Apparatus for selecting for temperature measurement that one of two masses whose temperature is the extreme in a certain direction. said apparatus comprising individual temperature-sensitive elements for producing electrical eflects proportional to the temperatures of the respective masses, means for comparing said electrical eifects in opposed relationship to obtain a resultant electrical eflect differentially representative of the opposed influences of said iirstnamed electrical eil'ects and of a polarity dependent upon the predominance of one of sai 13 opposed elects over the other, a measuring insh-ument. other temperature-sensitive elements pairlngsaidelanentsinoppomdrelatlonshipto obtain a resultant electrical eilect diflerentlally representative oi the opposed influences oithe electricaleilectsoicachofsaidpairsand oi'a pohrity dependent upon the p of one of said opposed effects over the other, other tlveelements individually and thermally associated with said, and means res imisive tothe resultant electrical eflect oi each of said pairs oi the ilrst mentioned temperatme-sehsitive elements for establishing a temperature-m connection to one of said other tunperature-sensitive elements in accordance with the polarity of said resultant efiect.

3. Apparatus for selecting for temperature t that one oi a plurality of masses whoeetempenitm'eisthe extremeinacertain direetlm'. said apparatus comprising individual tive elements adapted to produce electrical efl'ects proportional to the temperatures of the respective masses. means for pairing said elements in opposed 'rehtiopabip to obtain a resultant electrical effect diflerentially representative of the opposed hifluenoesoftheelcctrlcal eilectsoi'eachoi'said pairs and of a polarity dependent upon the predominance oi one of said opposed eflects over the other, a instrument. other term peraturedensitive elements individually and thermally amociated with said masses. and meam subject to the resultant electrical effect of each of said pairs of the first-mentioned temperative elements for connecting said t with one of said last-named elements in with the polarity of said resultant eil'cct.

4- Apparatus for selecting for temperature t that one of a plurality of masses whose temperature is the extreme in a certain direction, said apparatus comprising individual temperature-sensitive elements adapted to prodpce electrical efiects proportional to the temperaturcs of the respective masses, means for vely connecting a pair said elements in opposed relationship to obtain a resultant electrlcal eil'ect diflerentially representative of the olmoaed oi the electrical eiiects of said elements and of a polarity dependent upon the of one oi said opposed effects over the other, means responsive to said resultant electrical etlect and movable in a direction determined by the polarity oi said elect, a measuring t, other temperature-sensitive elements individually and thermally associated with said 1 means controlled by said re sponsive means for connecting said instrument with one of said last-named elements in accordance with the polarity of said resultant electrical effect to measure the temperature of the mass emaciated with one of said pair of said first-mentioned elements. and meansior connecting said 14 element of said pair to said responsive means in opposed relation to a further one of said ilrstmentioned elements.

5. Apparatus for selecting for temperature measurement that one of a plurality of masses whose temperature is the extreme in a certain direction, said apparatus comprising individual temperature-sensitive elements adapted to produce electrical elects proportional to the temperatures oi the respective masses, electromagnetic means movable in either 01' opposite directions in accordance with the direction of current flow therethrough. switching means (or successively coupling selected pairs of said elements in opposed relationship to said electromagnetic means, other temperature-sensitive elements individually and thermally associated with-said and relay means controlled by said electromagnetic means for establishing a temperature-measurmg connection with one of said other temperature-sensitive elements for measurement of the temperature of that one of said which has said extreme temperature.

6. Apparatus for selecting for temperature measurement that one of a plurality of masses whose temperature is the extreme in a certain direction. said apparatus comprising individual temperature-sensitive elements adapted to produce electrical efiects proportional to the temperatures oi the respective masses. a galvanometer operable in either of opposite directions in accordance with the direction of current flow 'therethrough, switching means for successively coupling selected pairs of said elements in opposed relatlonship to said galvanomcter, other temperature-sensitive elements individually and thermally associated with said masses, a plurality of relay means for establishing temperaturemeasuring connection to said other temperaturesensitive elements, and means controlled by said galvanometer for actuating the relay means corresponding to that one of said masses which has the extreme temperature in a certain direction.

7. Apparatus for selecting for temperature measurement that one of a plurality of masses whose temperature is the extreme in a certain direction, said apparatus comprising individual temperature-sensitive elements adapted to produce electrical effects proportional to the temperatures of the respective masses. electromagnetic means movable in either of opposite directions in accordance with the directions of current flow therethrough, switching means (or successively coupling selected pairs of said ele ments in opposed relationship to said electromagnetic means, other temperature-sensltive elements individually and thermally associated with said masses, relay means for establishing temperature-measuring connections to said other temperature-sensitive elements respectively, means controlled by said electromagnet means ior actuating the relay means corresponding to that one of said masses which has the extreme temperature in a certain direction, and means for maintaining the actuated relay means in actuated condition until another of said masses exceeds said temperature in said direction.

8. Apparatus for selecting for temperature rreasurement that one of a plurality of masses whose temperature is the extreme in a certain direction, said apparatus comprising individual temperature-sensitive elements adapted to produce, electrical eflects proportional to the temperatures of the respective masses. electromagnetic means movable in either of opposite directions in accordance with the direction of current now therethrough. a plurality of relays. one for each oi said temperature-sensitive elements. a plurality of banks of contacts, one bank for each of said temperature-sensitive elements. each bank having contacts connected respectively to opposite terminals of said elc means, each bank also having a contact connected to a corresponding one of said relays, switching means comprising contacts movable into t with said banks oi. contacts in predetermined succession, connections for placing the temperature-sensitive element corresponding to the bank of contacts engaged by said switching means into opposed relation with another temperance-sensitive element to thereby subject said electromagnetic means to the differential electrical elect of said elements. means responsive to operation of said electromagnetic means in a given direction and cooperating with said contact bank for bringing into action the relay connected to said bank. other temperature-sensitive elements individually and thermally associated with said masses, and means controlled by said relay for establishing a connection to one of said lastnamed elements for measurement of the temperature of the corresponding mass.

9. Apparatus for selecting for temperature measurement that one oi a plurality of masses whose temperature is the extreme in a certain direction. said apparatus comprising individual temperature-sensitive elements adapted to produce electrical eflects proportional to the temperatures of the respective u w electromagnetic means movable in either oi opposite directions in accordance with the direction or current flow therethrough, a plurality of relays, one for each oi said temperature-sensitive elements. a plurality of banks of contacts. one bank for each of said temperature-sensitive elements. each bank having contacts connected respectively to opposite terminals of said electromagnetic means, each bank also having a contact connected to a corresponding one of said relays, switching means comprising contacts movable into engagement with said banks of contacts in predetermined succession, connections for placing the tempera-. tore-sensitive element corresponding to the bank of contacts engaged by said switching means into opposed relation with another temperature sensitive element to thereby subject said electromagnetic means to the differential electrical eflect of said elements, means responsive to operation of said electromagnetic means in a given direction and cooperating with said contact bank for bringing into action the relay connected to said bank, other temperature-sensitive elements individually and thermally associated with said masses, means controlled by said relay upon actuation thereof for establishing a connection to one of said last-mentioned elements for measurement o! the temperature of the corresponding mass. and other means controlled by said relay for maintaining the latter in actuated condition until the temperature of another of said masses exceeds the temperature 01' said selected mass in a given direction.

10. Apparatus for selecting for temperature measurement that one of a plurality of whose temperature is the extreme in a certain direction, said apparatus comprising individual temperature-sensitive elements adapted to produce electrical eiiects proportional to the temperatures oi the respective I e a electromagrections in with the direction at current flow therethrough. a plurality o! relays.

for each of said temperature-scuttle apluralityoibanksoi'contaotnmebank each of said temperature-sensitive each bank having contacts respectively to opposite terminals of said meals. each bank also having a contact connected to a co one of said relays, switchnm means comprising contacts movable into with said banks of contacts in succession. for placing the temperature-sensitive element to the bulk or contacts en aged by said switchirm means into opposed relation with another tive element to thereby subiect said netic means to the diilerential elecn'ieal effect of said elements. means responsive to operation 01' said electromagnetic means in a dim direction and cooperating with said contactin briming intoaction therelayconneetedtosaidbank. other temperahrre-sensitive element individually and thermally associated with said masses, means controlled by said relay upon actuation tbeceoi' i'orestablishingatooneofsaidlastmentioned elements for t of the tenperature oi themandother connecting means controlled by said relay for connecting one terminal oi? the me 01 the first-mentioned temve elementstoacontactinthebank.

11. Apparatus for for tempm'ature mt that one of a plurality of moses whosetemperatureistheextremelnaoertain direction, said apparatus comprising individual temperature-sensitive elements adapted to produce electrical elects to the temperatures of the respective masses. electromagnetic means movable in either or opposite directionsinaccordancewith thedirectionoicurrent flow therethrough, a pluraiiqr of te l". one for each oi said temperature-smiths elements, apluralityotbanksoi'contactaonebankfor each oi said temperature-sensitive each bank having contacts connected respectively to opposite terminals or said el mean. eachbankalsohavingacontactconnectedto a corresponding one 01' said relays, switching means comprising contacts movable into engagement with said banks oi contacts in predetermined succession. connections for placing the temperature-sensitive element eorres to the bank of contacts engaged by said switching means into opposed relation with another termperature-sensitive element to thereby subject said electromagnetic means to the differential electric eii'ect oi said elements, each oi! said bank oi contacts further having acontact r by the switching means upon an additional movement oi the latter. means responsive to operation oi said electromagnetic means in a given direction and to engagement ofthe last mentionedcontaetoiabankhysaidswitchingmeans iorbrlngingintoactiontherelayto said bank. other temperature-sensitive elements individually and thermally associated with said masses, and means controlled by said relay for establishing a connection to one c! said lastnamed elements for measurement of the temperature of the co mass.

12. Apparatus for selecting for temperature measurement that one of a plurality of moses whosetemperatureistheextremeinacertam direction. said apparatus comprising individual netic means movable in either oi opposite ditemperature-sensitive elements adapted to produce electrical eflects proportional to the temperatures of the respective electromagnetic means movable in either or opposite directions in accordance with the direction of current flow therethrough, a plurality oi relays. one for each at said temperature-sensitive elements. a plurality 01 banks of contacts, one bank for each of said temperature-sensitive elements, each bank having contacts connected respectively to opposite terminals of said electromagnetic means. each bank also having a contact connected to a corresponding one of said relays, switching means comprising contacts movable into engagement with said banks of contacts in predetermined succession, connections for placing the temperature-sensitive element corresponding to the bank of contacts engaged by said switching means into opposed relation with another temperaturesensitive element to thereby subject said electromagnetic means to the differential electrical effect of said elements, means responsive to operation of said electromagnetic means in a given direction and cooperating with said contact bank for bringing into action the relay connected to said bank, other temperature-sensitive elements individually and thermally associated with said masses. and means controlled by said relay for establishing a connection to one of said last-mentioned elements for measurement oi the temperature of the corresponding mass. and means for operating said switching means at substantially constant speed into successive engagement with said contact banks.

13. In a system for measuring the temperature of a selected one of two masses, a set of temperature-sensitive elements adapted to produce electrical eilects proportional to the temperatures of the respective masses, means for comparing said eilects in opposed relationship to obtain a resultant electrical eflect ditlerentially representative oi the opposed influences of said first named electrical eil'ects and of a polarity dependent upon the predominance of one of said opposed eflects over the other, a second set of temperature-sensitive elements adapted to produce effects proportional to the temperatures of the respective masses, a measuring instrument, and means responsive to the aforesaid resultant electrical e1- !ect for connecting said instrument to one 01 the elements of said second set in accordance with the polarity of said resultant eflect.

14. In a system for measuring the temperature or a selected one of a plurality oi a iirst group 0! temperature-sensitive elements adapted to produce electrical effects proportional to the temperatures of the respective masses. means for progressively pairing said elements in opposed relationshi to obtain a resultant electrical effect diil'erentially representative oi the opposed iniluences oi the electrical effects 01 each 0! said pairs and of a polarity dependent upon the predominance of one 01' the opposed eflects over the other, a second group oi temperature-sensitive elements adapted to produce efiects proportional to the temperatures of the respective misses. a measuring instrument, and means responsive to the resultant electrical effect of each of said pairs of elements of the first group for connecting said measuring instrument with an element of the second group in accordance with the polarity of said resultant eilect.

15. In a system for measuring the temperature of a selected one of a plurality of masses, a first group oi temperature-sensitive elements adapted to produce electrical effects proportional to the temperatures of the respective masses, electromagnetic means movable in either or opposite directions in accordance with the direction of current flow therethrough, switching means for connecting different pairs or said elements in succession to said electromagnetic means with the elements of each pair in opposed relationship to subiect said electromagnetic means to the resultant electrical eflect of said opposed elements, relay means controlled by said electromagnetic means, a measuring instrument, a second group of temperature-sensitive elements adapted to produce etl'ects proportional to the temperatures oi. the respective masses, and means controlled by said relay means ior connecting said instrument with an element in said second group in accordance with the polarity of said resultant eflect.

18. In a system for measuring the temperature of a selected one of two masses, a set of temperatare-sensitive elements adapted to produce electrical eflects proportional to the temperatures 01' the respective masses, means for comparing said effects in opposed relationship to obtain a result ant electrical efiect diflerentially representative of the opposed influences of said first-named electrical effects and oi a polarity dependent upon the predominance oi one of said opposed eilects over the other, a second set of temperature-sensitive elements adapted to produce electrical e1- iects proportional to the temperatures of the respective masses. an electrical measuring instrument, and means responsive to the aforesaid resultant efiect for electrically connecting said instrument to one oi the elements or said second set in accordance with the polarity oi. said resultant effect.

17. In a system for measuring the temperature 01 a selected one of a plurality of masses, 9. first group 01' temperature-sensitive elements adapted to produce electrical eiIects proportional to the temperatures 01' the respective masses. electromagnetic means movable in either of opposite directions in accordance with the direction of current ilow therethrough, switching means for connecting different pairs 01' said elements in succession to said electromagnetic means with the elements of each pair in opposed relationship to subject said electromagnetic means to the resultant electrical efl'ect of said opposed elements, relay means controlled by said eletcromagnetic means, an electrical measuring instrument, a second group of temperature-sensitive elements adapted to produce electrical eflects proportional to the temperatures of the respective masses, and means controlled by said relay means for electrically connecting said instrument with an element in said second group in accordance with the direction oi operation of said electromagnetic means.

18. In a system for measuring the temperature oi a selected one of a plurality of masses, a group at temperature-sensitive elements adapted to produce electrical eilects proportional to the temperatures of the respective masses, a galvanometer operable in either of opposite directions in accordance with the direction of current flow therethrough, switching means ior successively applying to said galvanometer the net voltages of selected pairs oi said temperature-sensitive elements connected in opposition to thereby actuate said galvanometer in a direction dependent upon the relative temperatures of opposed couples, a second group of temperature-responsive elements adapted to produce electrical eflects proportional to the temperatures of said respective masses. an

19 electrical measuring instrument, and relay means controlled by said galvanometer tor establishing a connection between said instrument and a temperature sensitive element of said second group in accordance with the direction of actuation 0! said galvanometer.

19. In a system for measuring, the temperature of a selected one oi a plurality of masses, a group of temperature-sensitive elements adapted to produce electrical eflects proportional to the temperatures oi the respective masses, 0. galvanometer operable in either of opposite directions in accordance with the direction 0! current flow therethrough. switching means tor successively connecting in series opposition selected pairs of said temperature-sensitive elements and applying their combined electrical effects to said galvanometer to actuate the same in a direction dependent upon the relative magnitude or said electrical effects, a second group of temperature-sensitive elements adapted to produce eflects pro- Ntion.

JAMES N. STEWART.

REFERENCES CITED The following references are of record in the tile or this patent:

UNITED STATES PATENTS Name Date Taylor Sept. 9, 1930 Martin Sept. 16, 1930 Simpson Jan. 10, 1933 Boston July 6, 1948 Number 

